Aluminum brazing sheet

ABSTRACT

An aluminum brazing sheet has a core material made of an aluminum alloy and a cladding material cladded on at least one side of the core material and made of an aluminum alloy having a potential lower than that of the core material. The cladding material is made of an aluminum alloy consisting essentially of 0.4 to 0.7 mass % of Mg, 0.5 to 1.5 mass % of Si, and 0.4 to 1.2 mass % of Mn, the remainder being Al and unavoidable impurities. Zn in the amount of 6 mass % or less is added in accordance with need. An aluminum brazing sheet having not only high strength but also less pressure adhesion failure and excellent productivity can be obtained.

TECHNICAL FIELD

The present invention relates to an aluminum brazing sheet employed in aheader, a side plate, and the like of an automobile radiator and, inparticular, to an aluminum brazing sheet for brazing having highstrength, high formability, and also excellent productivity.

BACKGROUND ART

Conventionally, an aluminum brazing sheet for brazing has been employedin a header, a side plate, and the like of an automobile radiator, andan Al—Mn based aluminum alloy such as JIS3003 has been employed as acore material. Also, an Al—Si based aluminum alloy such as JIS4045 orJIS4343 has been employed as a brazing material, and an Al—Zn basedaluminum alloy has been employed as a cladding material which serves asa sacrificial anode. However, the post-braze strength of the brazingsheet employing an Al—Mn based alloy such as JIS3003 serving as a corematerial is about 110 N/mm², which is not sufficient for a brazingsheet. In addition, the above brazing sheet does not have sufficientcorrosion resistance. In order to improve the post-braze strength, theaddition of Mg to a core material is effective. However, when such amaterial is employed for brazing together with a flux which generates abrittle compound through reacting with Mg, particularly, as in Nocolokbrazing, the brazeability of the brazing sheet in which Mg is added to acore material is significantly deteriorated. Therefore, the addition ofMg to a core material is not preferable.

On the other hand, about 2 mass % of Mg has been added to a claddingmaterial (see Japanese Patent Laid-Open Publications Nos. 2000-210787and 2000-87163). In this case, Mg added to a cladding material diffusesfrom the cladding material to a core material during heating forbrazing. At the same time, Si diffuses from a brazing material to thecore material and is combined with Mg to form Mg₂Si. Therefore, thestrength can be improved through the addition of Mg to a claddingmaterial.

However, when the above cladding material with high Mg content islaminated with a core material through clad-rolling processing, ablister may be formed on the product surface due to pressure adhesionfailure. This results in lower yields of products, so that theproductivity is lowered.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an aluminum brazingsheet having not only high strength but also less pressure adhesionfailure during clad-rolling and also excellent productivity.

The aluminum brazing sheet according to the present invention comprisesa core material made of an aluminum alloy and a cladding materialcladded on at least one side of the core material and made of analuminum alloy having a potential lower than that of the core material,wherein the cladding material is made of an aluminum alloy consistingessentially of 0.4 to 0.7 mass % of Mg, 0.5 to 1.5 mass % of Si, and 0.4to 1.2 mass % of Mn, the remainder being Al and unavoidable impurities.

According to the present invention, by suppressing the content of Mg inthe cladding material and adding both of Si and Mn to the claddingmaterial, the pressure adhesion failure during clad-rolling processingcan be prevented, and also the strength can be satisfactorily improved.Therefore, a high-quality aluminum brazing sheet with excellentproductivity can be obtained.

In the aluminum brazing sheet of the present invention, the claddingmaterial preferably further contains Zn in the amount of 6 mass % orlower. For example, the cladding material is cladded on one side of thecore material, and a brazing material is laminated on the other side ofthe core material.

Preferably, the Si content of the aluminum alloy constituting thecladding material is in the range of 0.6 to 0.9 mass %.

Preferably, the Mn content of the aluminum alloy constituting thecladding material is in the range of 0.6 to 1.0 mass %.

Further, the core material preferably contains 0.3 to 0.7 mass % of Si,0.6 to 1.2 mass % of Mn, and 0.5 to 1.0 mass % of Cu.

Examples of the unavoidable impurities contained in the claddingmaterial of the present invention include Fe, Cu, Cr, Ti, and Be. Theupper allowable limits of the above elements are 0.5 mass % for Fe, 0.2mass % for Cu, 0.3 mass % for Cr, 0.2 mass % for Ti, and 10 ppm for Be,respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will next be described in more detail. A claddingmaterial has the composition whose potential is lower than that of acore material, and a certain potential difference is maintained betweenthe cladding material and the core material.

In such a cladding material conventionally employed, a large amount ofMg has been added to improve the strength. However, in the presentinvention, the amount of Mg added to a cladding material issignificantly reduced to 0.7 mass % or less, and the reduction in thestrength due to the reduction in the added amount of Mg is complementedby the addition of Si and Mn. Since the added amount of Mg is small, thegeneration of pressure adhesion failure such as a blister may beprevented upon laminating the core material and the cladding materialthrough rolling working. In this manner, the high strength and highproductivity of an aluminum brazing sheet can be implemented by reducingthe added amount of Mg and by the addition of Si and Mn.

Hereinafter, the reasons for adding each component to the claddingmaterial and for defining the composition will be described.

Mg: 0.4 to 0.7 mass %.

Mg is added to the cladding material in the range of 0.4 mass % or moreto obtain sufficient strength. In order to obtain higher strength, Mg ispreferably added in a large amount. However, when a large amount of Mgis added, pressure adhesion failure such as a blister is generatedduring clad-rolling in a manufacturing process. Therefore, the addedamount of Mg must be 0.7 mass % or less.

Si: 0.5 to 1.5 mass %, preferably 0.6 to 0.9 mass %.

Si is added to the cladding material together with Mn for complementingthe strength thereof. When the added amount of Si is less than 0.5 mass%, the strength is not effectively improved. When the added amount of Siexceeds 1.5 mass %, burning is likely to take place since the additionof Si lowers the melting point. In addition, a Si-based intermetalliccompound is formed, thereby lowering the rolling workability.Preferably, the added amount of Si is in the range of 0.6 to 0.9 mass %.

Mn: 0.4 to 1.2 mass %, preferably 0.6 to 1.0 mass %.

Mn is added to the cladding material together with Si for complementingthe strength. When the added amount of Mn is less than 0.4 mass %, thestrength is not effectively improved. On the other hand, when the addedamount of Mn exceeds 1.2 mass %, large precipitates containing Mn aregenerated, resulting in the formation of microcracks during rollingworking. Preferably, the added amount of Mn is in the range of 0.6 to1.0 mass %.

Zn: 6 mass % or less.

When an aluminum alloy having a low potential is employed as a corematerial, the addition of Zn to the cladding material is effective forobtaining the potential of the cladding material lower than that of thecore material. The addition of Zn to the cladding material results inlowering the potential thereof, thereby effectively allowing thepotential of the cladding material to be lower than that of the corematerial. In this case, when the added amount of Zn exceeds 6 mass %,the rolling workability is likely to be lowered which is not preferable.

In order to fully obtain the sacrificial anode effect of claddingmaterial, the potential of the core material must be higher than that ofthe cladding material. Therefore, the composition of the core materialis selected such that the potential thereof is higher than that of thecladding material. For example, an Al-0.5Si-0.8Cu-1.2Mn alloy (in mass%) may be employed. Since Mg contained in the core material enhances thestrength of the core material, Mg may be added to the core material upto 0.3 mass % up to which the brazeability is not inhibited.

A preferred aluminum alloy serving as the core material contains 0.3 to0.7 mass % of Si, 0.6 to 1.2 mass % of Mn, and 0.5 to 1.0 mass % of Cu.Further, Cr (less than 0.15 mass %) and Ti (less than 0.2 mass %) may beselectively added to the core material.

Examples of the layered structure of the brazing sheet include atwo-layer sheet in which one side of the core material is cladded withthe cladding material having the above composition, and three-layersheet in which one side of the core material is cladded with the abovecladding material and the other side is cladded with a brazing material.

No particular limitation is imposed on the composition of the brazingmaterial. For example, an Al—Si based alloy such as JIS4045 alloy and anAl—Si—Zn based alloy may be employed. Any cladding ratio between thecladding material/core material/brazing material during cladding may beemployed in accordance with the required properties of the applied part.

Examples of the present invention and Comparative Examples will next bedescribed, and the advantages of the present invention will also bedescribed. Cladding materials having compositions shown in Table 1 wereprepared. Each of the prepared cladding materials was cladded with acore material (an Al-0.5Si-0.8Cu-1.2Mn alloy with additives of Cr (0.1mass %) and Ti (0.15 mass %)) and a brazing material (JIS4045) with acladding ratio of cladding material (10%)/core material (80%)/brazingmaterial (10%), to obtain a three-layer cladding sheet having a finalthickness of 1.2 mm. The pressure adhesion property was evaluatedthrough visual observation of a blister generated on the surface of thecladding sheet having a width of 200 mm and a length of 1,000 mm. Theportion around the blister was removed from the product, and thepressure adhesion property was represented by “O” in Table 1 if theyield was 90% or more. The pressure adhesion property was represented by“Δ” if the yield was 80 to 90%, and was represented by “x” if the yieldwas less than 79%. The cladding sheet was cut into a size of 100 mm inwidth and 230 mm in length, followed by brazing heating through holdingthe cut cladding sheet at 600□ for 5 minutes in nitrogen gas. Thethus-prepared sheet was subjected to a tensile test (JISZ2201) tomeasure the post-braze strength. The post-braze strength is representedby “O” in Table 1 if the tensile strength is 160 Mpa or more.

TABLE 1 Composition of cladding Post- Pressure material brazing adhesionNo. Mg Si Mn Zn strength property Example 1 0.52 0.71 0.89 2.26 ∘ ∘ 20.50 0.81 0.91 2.13 ∘ ∘ 3 0.39 0.64 0.51 2.82 ∘ ∘ 4 0.59 0.66 0.49 2.60∘ ∘ 5 0.7 1.2 1.2 2.5 ∘ ∘ 6 0.3 0.5 0.4 1.5 ∘ ∘ 7 0.3 1.2 1.2 0.3 ∘ ∘ 80.56 0.68 0.51 3.82 ∘ ∘ 9 0.6 0.7 0.5 6.0 ∘ ∘ 10 0.5 0.85 1.0 — ∘ ∘ 110.6 0.7 0.5 7.0 ∘ Δ Comp- 12 2.20 0.06 0.00 1.5 ∘ x arative 13 0.53 0.020.00 1.34 x ∘ Example 14 2.20 0.06 0.00 1.5 ∘ x 15 0.53 0.02 0.00 1.34 x∘ 16 0.3 0.4 0.4 1.5 x ∘ 17 0.7 0.4 1.2 1.5 x ∘~Δ 18 0.2 1.2 1.2 1.5 x ∘19 0.7 1.2 0.3 1.5 x ∘~Δ 20 0.8 0.5 0.4 0.5 ∘ x 21 0.5 2.0 0.4 1.5 Testx piece unable to be processed 22 0.5 1.0 1.4 0.5 Test x piece unable tobe processed

As shown in Table 1, the aluminum brazing sheet of Examples 1 to 11 hadexcellent cladding pressure adhesive property and post-braze strengthsince the composition of the cladding material falls within the scope ofthe claims of the present invention. On the other hand, the aluminumbrazing sheet of Comparative Examples 12, 14, and 20 had lower pressureadhesive property due to the high content of Mg. The aluminum brazingsheet of Comparative Examples 13 and 15 had insufficient post-brazestrength since the Mn content is too low. The post-braze strength wasunsatisfactory in Comparative Examples 16 and 17 since the Si content istoo low and also in Comparative Examples 18 since the Mg content is toolow and in Comparative Example 19, since the Mn content is too low.Since the aluminum brazing sheet of Comparative Example 21 had lowrolling workability due to the high content of Si, a test piece for thetensile test was unable to be processed. A crack was generated in thealuminum brazing sheet of Comparative Example 22 during rolling sincethe content of Mn is too high, and thus a test piece for the tensiletest was unable to be processed.

1. An aluminum brazing sheet consisting of: a core material made of analuminum alloy; a cladding material cladded on one side of the corematerial; and a brazing material laminated on the side of the corematerial opposite to the cladding material; wherein a potential of thecladding is lower than a potential of the core and a sacrificial anodeeffect is obtained, the cladding material is an aluminum alloyconsisting of from 0.52 to 0.7 mass % of Mg, 0.5 to 1.5 mass % of Si,0.4 to 1.2 mass % of Mn, 0.3 to 6 mass % of Zn, Al, and the corematerial consists of: 0.3 to 0.7 mass % of Si, 0.6 to 1.2 mass % of Mn,0.5 to 1.0 mass % of Cu, a maximum of 0.3 mass % Mg, from 0.15 to 0.2mass % Ti, from 0.1 to 0.15 mass % Cr, and Al.
 2. The aluminum brazingsheet according to claim 1, wherein the Si content of the claddingmaterial is in a range of 0.6 to 0.9 mass %.
 3. The aluminum brazingsheet according to claim 1, wherein the Mn content of the claddingmaterial is in a range of 0.6 to 1.0 mass %.
 4. The aluminum brazingsheet according to claim 2, wherein the Mn content of the aluminum alloyconstituting the cladding material is in a range of 0.6 to 1.0 mass %.5. The aluminum brazing sheet according to claim 1, wherein the Zncontent of the cladding material is 2.0 to 6.0 mass %.